The present invention relates to golf balls having a portion or layer formed from a polymeric composite that preferably includes at least two polymers with distinct microstructures. In particular, the balls can include a polybutadiene having at least about 80 percent cis-isomer polybutadiene blended with a polybutadiene having at least about 50 percent trans-isomer polybutadiene. Methods of preparing such golf balls are also recited.
Multi-layer golf balls contain a core, which may include one or more layers of solid material or one or more layers of solid material encompassing a fluid therein, and a cover. Optionally, an elastic winding may also be used to form a layer surrounding the center to provide certain playing characteristics. Such balls are known as xe2x80x9cwoundxe2x80x9d balls. The multi-layer golf balls discussed herein include a core and a cover. The terms xe2x80x9ccorexe2x80x9d or xe2x80x9cball core,xe2x80x9d as used herein, include a center having one or more layers and an intermediate layer formed of one or more layers. The terms xe2x80x9ccenterxe2x80x9d or xe2x80x9cball center,xe2x80x9d as used herein, include a solid and/or fluid mass around which an intermediate layer and a cover are disposed. The intermediate layer is disposed between the center and the cover, typically in concentric fashion, with the cover being the outermost portion of the ball.
A variety of golf ball compositions are known and used in various methods of manufacture. Unfortunately, these compositions and methods tend to produce balls that do not consistently achieve a symmetrical core. See, for example, the discussion in U.S. Pat. No. 6,056,842, which illustrates the poor centering that occurs in conventionally formed golf balls. Multi-layer ball production has been plagued by center portions that become off-centered during the manufacture of such balls. Off-center golf balls are a hindrance to many players, particularly those able to achieve great control using a symmetrical ball. This lack of symmetry is now believed to be caused, at least in part, by the materials and methods conventionally used in forming multi-layer golf balls.
Compositions typically including greater than 40 percent cis-1,4-polybutadiene isomer are often used in forming golf ball cores, or a portion thereof. Unfortunately, many cis-polybutadiene materials are fairly soft prior to crosslinking, which can lead to the off-centering problems noted above. A number of references disclosing various cis-polybutadiene materials are discussed below.
U.S. Pat. Nos. 3,896,102; 3,926,933; 4,020,007; and 4,020,008 disclose a 1,3-butadiene component and a method and catalyst for preparing trans-polybutadiene, and that it is well known that increasing content of trans-polybutadiene is more resinous and produces a more elastic, tough, crystalline, thermoplastic solid. The ""933 and ""008 patents further disclose that trans-polybutadiene is resistant to attack by ozone and other chemical agents, and is typically used in insulation, battery cases, and golf ball covers.
U.S. Pat. No. 4,020,115 discloses the preparation of homopolymers and random copolymers of butadiene with styrene and/or isoprene that include butadiene units having a low vinyl content of not over 12 percent and a trans-polybutadiene structure of from about 70 to 81 percent. These polymers are disclosed to have broad molecular weight distribution, as well as tack and green-strength desired for manufacturing tires. A variety of trans-polybutadiene and vinyl-polybutadiene materials are also disclosed with the catalysts used for the preparation thereof.
U.S. Pat. No. 4,919,434 discloses a two-piece golf ball having a solid core of more than 40% cis-1,4-polybutadiene isomer and a cover having an inner layer of 0.1 to 2 mm thickness and an outer layer of 0.1 to 1.5 mm thickness. The inner layer is a thermoplastic resin, such as an ionomer, polyester elastomer, polyamide elastomer, thermoplastic urethane elastomer, propylene-butadiene copolymer, 1,2-polybutadiene, polybutene-1, and styrene-butadiene block copolymer, either individually or in combination.
U.S. Pat. No. 4,929,678 discloses a rubber composition for golf balls including at least 40 percent by weight polybutadiene rubber with a Mooney viscosity of 45 to 90 and a cis-bond content of at least 80 percent, a co-crosslinking agent, and a peroxide. These polymers are disclosed to have a dispersity of between 4.0 to 8.0, which is a ratio of weight average molecular weight to number average molecular weight.
U.S. Pat. No. 4,931,376 discloses butadiene polymers and copolymers with another conjugated diene having at least 80 percent butadiene by weight; 60 to 98 percent trans-polybutadiene linkages; a molecular weight distribution of 1.1 to 4.0; melting temperature of 40xc2x0 C. to 130xc2x0 C.; and a content of insolubles in boiling cyclohexane of 1% or less, as well as processes for making the same. Weight average molecular weights of 30,000 to 300,000 and trans-polybutadiene contents greater than about 30 percent are preferred. These materials are disclosed for use in golf ball covers, splint or gyps material, and the like.
U.S. Pat. No. 4,955,613 discloses golf balls made from two polybutadienes, each having a Mooney viscosity below about 50 and a cis-polybutadiene isomer content of greater than about 40 percent, more preferably greater than about 90 percent, and catalysts for preparing the polybutadienes.
U.S. Pat. No. 4,971,329 discloses solid golf balls made from polybutadiene mixtures of about 99.5 to 95 weight percent cis-1,4-polybutadiene and about 0.5 to 5 weight percent vinyl-1,2-polybutadiene. The cis-polybutadiene is made by blending from about 80 percent to 100 percent by weight of cis-polybutadiene with a cis-content of 95 percent and about 0 weight percent to 20 weight percent of cis-polybutadiene with a cis-content of about 98 percent.
U.S. Pat. No. 5,553,852 discloses three-piece solid golf balls having a center core, intermediate layer, and cover. The center core is prepared with a 1,4-polybutadiene containing more than 90% cis-polybutadiene isomer for high repulsion, co-crosslinking agent(s), peroxide, and other additives.
U.S. Pat. No. 5,833,553 discloses core compositions including polybutadiene, natural rubber, metallocene catalyzed polyolefins, polyurethanes, and other thermoplastic or thermoset elastomers, and mixtures thereof having a broad molecular weight range of 50,000 to 500,000, preferably from 100,000 to 500,000. Polybutadiene with a high cis-content is noted as being preferred.
U.S. Pat. No. 5,861,465 discloses thread rubber for wound golf balls having rubber component obtained by vulcanizing rubber composition including rubber selected from natural rubber, synthetic high-cis-polyisoprene rubber, and mixtures with at least one specific diaryl disulfide, a vulcanizing agent, and an antioxidant.
U.S. Pat. No. 6,018,007 discloses the preparation of trans-polybutadiene and other polymers and copolymers having trans configuration in the conjugated diene monomer contributed units with improved catalyst systems. The resulting polymers are rubbery, except those with high trans content, and may be vulcanized by well known methods and incorporated in tires, general rubber goods, and plastics materials.
U.S. Pat. No. 6,130,295 discloses a two-piece golf ball having an unvulcanized cover that includes a mixture of ionomer and polybutadiene having a trans-isomer content of at least 60 percent.
It is desirable to reduce the off-centering problem and manufacturing inconsistencies found in many conventional golf balls, although little notice has been taken of this important part of golf ball manufacture until recently. In part, many materials are difficult to work with before they have been crosslinked. The polymers typically used in the core, particularly in intermediate layers or shells, tend to have a memory that urges the polymer back to its earlier or original shape, which necessitates rapid compression molding to crosslink the polymer as soon as the shells are formed.
It is also understood that there has been great difficulty in the art when attempting to blend certain polymer materials having different microstructures, e.g., polybutadiene and polyisoprene. Thus, it is desired to find an improved composition and method for providing such composition, for use in manufacturing golf balls that reduces or avoids the disadvantages present when using conventional materials for golf balls.
The invention relates to a golf ball including a polymeric composite which comprises at least one polybutadiene. In a first embodiment, the polymeric composite is formed from a material including at least two polymers, for example, polybutadiene and polyisoprene. In a second embodiment, the polymeric composite is formed from a material including at least one polybutadiene and a plurality of nanoparticles. In one embodiment, the polymeric composite has less than about 5 percent vinyl-isomer content in the polybutadiene. In a preferred embodiment, the polymeric composite has less than about 3 percent vinyl-isomer content in the polybutadiene. In another embodiment, the polymeric composite has at least about 20 percent trans-isomer content in the polybutadiene. In one preferred embodiment, the polymeric composite has a molecular weight of at least about 200,000 and a polydispersity of less than about 3. To achieve high resilience, it is preferred in one embodiment that each polymeric material in the polymer composite have a molecular weight of at least about 200,000 and a polydispersity of less than about 3. In an embodiment where processability improvements are more important, however, each polymer material preferably has a different molecular weight. In one such preferred embodiment, the difference in molecular weight is at least about 100,000.
In one preferred embodiment, the polymeric composite includes a plurality of nanoparticles having an average size of less than about 5000 nm. Nanoparticles are one possible method to alter the modulus of materials used to form one or more layers of a ball, as they permit adjustment of density, COR, and mixing time. In a preferred embodiment, the polymeric composite includes nanoparticles and a coupling agent. Preferred coupling agents include silanes, titanates, and sulfides. In one embodiment, the nanoparticles include silica.
In another embodiment, the golf ball includes at least two layers and the polymeric composite is disposed in at least one of the two layers. In another embodiment, the polymeric composite is disposed in a core of the golf ball. In yet another embodiment, the polymeric composite is disposed in a cover layer of the golf ball. The polymeric composite can also be disposed in an elastomeric thread that forms a layer in the golf ball, either alternatively or in addition to the above-noted embodiments.
In one embodiment, the polymeric composite comprises at least one polyisoprene polymer. In a preferred embodiment, the at least one polyisoprene polymer has a trans-isomer content of at least about 10 percent. One preferred embodiment includes a polymeric composite including a blend of the at least one polyisoprene polymer and at least one polybutadiene polymer in at least a portion of a golf ball.
In one embodiment, the effective modulus of a core including the crosslinked polymeric composite is less than about 110 MPa (xcx9c16,000 psi). In one alternate embodiment, the effective modulus of a core including the crosslinked polymeric composite is less than about 55 MPa (xcx9c8000 psi). In another embodiment, the coefficient of restitution of a core including the polymeric composite is greater than about 0.8. In yet another embodiment, the flexural modulus of an uncrosslinked compound including the polymeric composite is greater than about 3.5 MPa.
The invention also relates to a method of preparing the above-described golf ball by combining a first polybutadiene cement having at least about 50 percent trans-isomer content and a second polybutadiene cement having at least about 90 percent cis-isomer content to form a first mixture, evaporating at least substantially all of the solvent from the first mixture to obtain a polymeric composite, combining the polymeric composite with at least one crosslinking agent to obtain a second mixture, and forming the second mixture into at least a portion of the golf ball.
In one embodiment, the forming includes injection molding. In one embodiment, the first polybutadiene cement has been polymerized in the presence of a sufficient amount of cobalt-catalyst to increase the trans-isomer content of the polybutadiene. In another, preferably alternative, embodiment, at least one of the polybutadiene cements has been polymerized in the presence of a sufficient amount of nickel or neodymium catalyst to increase the molecular weight of the cement.
The invention also relates to a golf ball including a polymeric composite which includes a first polybutadiene having at least 90 percent cis-isomer, a second polybutadiene having at least 70 percent trans-isomer, and a plurality of nanoparticles, wherein the polymeric composite includes a polybutadiene having less than about 5 percent vinyl-isomer content. In one embodiment, the second polybutadiene has less than about 50 percent trans-isomer content.
The invention also relates to a golf ball where the flexural modulus of the uncrosslinked polymeric composite is greater than about 3.5 MPa.